Extrusion coating involves the process of extruding a molten film from a die and contacting this molten film with a substrate under pressure in the nip of two counter-rotating rolls or the like. Both of these rolls can be chill rolls, which by definition means temperature controllable rolls. Alternatively, one of these rolls can be a pressure roll, which has a deformable surface able to distribute pressure over an uneven surface. The pressure roll is in contact with the side not being coated, and the chill roll is in contact with the side being coated.
Extrusion coating of woven and non-woven polyolefin substrates involves several problems. Some examples of such problems are extruder surging, poor coating adhesion particularly to polypropylene, and unaesthetic hand for some coatings having a thickness greater than one mil. To decrease extruder surging, which is the non-uniformity of gauge or coating weight in the machine direction, and to increase adhesion of the extruded coating to polypropylene substrates, the melt flow rate of the extrusion coating is generally increased. However, to decrease undesirable neck-in which is the difference between the width of the web as it exits from a die and that width at the point of contact with a substrate, the melt flow and temperature of the extruded coating are generally decreased. In summary, to achieve a suitable extrusion coating for polyolefins and more specifically polypropylene, the range of temperatures and flow rates that are usable must resolve a variety of problems which have conflicting methods of solution.
Good adhesion with extrusion coatings of low density plyethylene to high density polyethylene fabrics requires extrusion temperatures of about 600.degree. F. in order to cause some melt oxidation. However, neither low density nor high density polyethylene alone can be made to adhere well to polypropylene fabrics regardless of process conditions. Surface primers for polypropylene fabrics have had limited success.
In U.S. Pat. No. 3,524,759 (1970) of R. L. McConnell et al., a process for curtain coating of flat sheets, paper, cardboard, articles of any size or shape, etc. is disclosed. The composition employed in that curtain coating process was a thermoplastic composition having a melt viscosity of 190.degree. C. of 5,000 to 125,000 cp. comprising:
(1) 40 to 99 percent by weight of a copolymer of 55 to 99 percent by weight of ethylene and 1 to 45 percent of at least one comonomer selected from the group consisting of: PA1 (2) 1 to 60 percent by weight of a crystallizable polymer of an .alpha.-olefin having 2 to 10 carbon atoms, said polymer having a melt viscosity at 190.degree. C. of 1,000 to about 20,000 cp. when the polymer is polyethylene and a melt viscosity at 190.degree. C. of 1,000 to about 400,000 cp. when the polymer is polypropylene or other higher polyolefin homo- or copolymer. In preferred embodiments of this invention, the melt viscosity of the coating composition is at least 15,000 cp. and the copolymer is ethylene/vinyl acetate. PA1 (a) about 50-90% and preferably about 60-80% by weight of a terpolymer containing reacted ethylene, propylene, and a diene, said terpolymer having a flow rate in the range of about 0.5 to 1.0 g/10 min. and preferably in the range of about 0.6 to 0.7 g/10 min. (ASTM D-1238-70 Condition L), wherein the diene is in a low concentration up to a maximum concentration in percent by weight of about 3% and is a monomer selected from the group consisting of 1,3-butadiene, isoprene, chloroprene, cyclooctadiene-1,5, dicyclopentadiene, cyclododecatriene-1,5,9, cyclododecadiene-1,7, cycloheptadiene-1,4, cyclohexadiene-1,4, norbornadiene, methylene-norbornene, methyl-tetrahydroindene, dimethyl-tetrahydroindene, 6-methyl-heptadiene-1,5, hexadiene-1,4, 6-methyl-4,7,8,9-tetrahydroindene, and ethylidene-norbornene, and wherein the reacted ethylene and propylene are in a ratio by weight of about 3:1, PA1 (b) about 50-10% and preferably about 40-20% by weight of a high density polyethylene having a melt index in the range of about 0.2-30 g/10 min. and preferably in the range of about 10-20 g/10 min. (ASTM D-1238-65T Condition E), an unannealed density in the range of about 0.956-0.965, a weight average molecular weight in the range of about 50,000-200,000, and optionally PA1 (c) one or more of the additional components selected from the group consisting of: PA1 (a) about 30-75% and preferably about 30-50% by weight of an olefin polymer blend, disclosed in U.S. Pat. No. 3,887,640 (1975) which patent is incorporated herein by reference, this blend comprises about 40 to 99 and preferably about 75 to 97 percent by weight of an ethylene-propylene block copolymer comprising at least about 80 percent by weight polymerized propylene having a flow rate of about 15 dg/min. to 100 dg/min. and preferably of about 25 dg/min. to 95 dg/min. as determined by ASTM D-1238-62T and about 1 to 60 and preferably about 2.5 to 25 percent by weight of polyethylene having a melt index recovery of at least about 50 and a density greater than about 0.912, PA1 (b) about 70-25% and preferably about 50-30% by weight of an ethylene-isobutylacrylate copolymer having a flow rate in the range of about 50 to 90 g/10 min. (ASTM D-1238-70 Condition L) and a density at 23.degree. C. in the range of about 0.920-0.930, and comprising about 30% by weight of reacted isobutylacrylate and optionally, PA1 (c) one or more of a variety of additional components selected from the group consisting of: PA1 (a) about 30-50% and preferably about 35-45% by weight of an ethylene-isobutylacrylate copolymer having a flow rate in the range of about 50-90 g/10 min. (ASTM D-1238-70 Condition L), and a density at 23.degree. C. in the range of about 0.920-0.930, and comprising about 30 percent by weight of reacted isobutylacrylate, PA1 (b) about 10-40% and preferably about 25-35% by weight of a terpolymer comprising reacted ethylene, propylene, and a diene, said terpolymer having a flow rate in the range of about 0.5 to 1.0 g/10 min. and preferably in the range of about 0.6 to 0.7 g/10 min. (ASTM D-1238-70 Condition L), wherein the diene is in a low concentration up to a maximum concentration in percent by weight of about 3% and is a monomer selected from the group consisting of 1,3-butadiene, isoprene, chloroprene, cyclooctadiene-1,5, dicyclopentadiene, cyclododecatriene-1,5,9, cyclododecadiene-1,7, cycloheptadiene-1,4, cyclohexadiene-1,4, norbornadiene, methylene-norbornene, methyl-tetrahydroindene, dimethyl-tetrahydroindene, 6-methylheptadiene-1,5, hexadiene-1,4, 6-methyl-4,7,8,9-tetrahydroindene, and ethylidene-norbornene, and wherein the reacted ethylene and propylene are in a ratio by weight of about 3:1, PA1 (c) about 10-40% and preferably about 25-35% by weight of a high density polyethylene having a melt index in the range of about 0.2-30 g/10 min. and preferably in the range of about 10-20 g/10 min. (ASTM D-1238-65T Condition E), an unannealed density in the range of about 0.956-0.965, a weight average molecular weight in the range of about 50,000-200,000, and optionally, PA1 (d) one or more of the additional components selected from the group consisting of: PA1 1. being substantially non-volatile from a resionous polyolefin polymer matrix at the approximate melting point of a polymer composition comprising said resinous polyolefin polymer, antimony trioxide, and said halogenated organic compounds, PA1 2. having a gram molecular weight above about 200; and PA1 3. a halogen content in percent by weight of the halogenated compound in the range of about 35-93% wherein the halogen is selected from the group consisting of chlorine and bromine.
(a) alkenyl alkanoates wherein said alkenyl portion contains 2-4 carbon atoms and said alkanoate portion contains 2-6 carbon atoms, PA2 (b) alkyl acrylates, wherein said alkyl contains 1 to 8 carbon atoms, PA2 (c) alkyl methacrylates wherein said alkyl contains 1 to 8 carbon atoms, PA2 (d) acrylic acid, PA2 (e) methacrylic acid, and PA2 (1) about 0-10% and preferably about 0.5-5% by weight of an opacifier such as TiO.sub.2 able to pass through a 200 mesh screen, and preferably through a 325 mesh screen, PA2 (2) about 0-20% and preferably about 0.5-15% by weight of a fire retardant composition comprising one or more poly-halogenated organic compounds and antimony trioxide, PA2 (3) about 0-5% and preferably about 0.5-3% by weight of an ultraviolet light stabilizer for polyolefins such as nickel dibutyl dithiocarbamate, 2-(2-hydroxy-5-t-octylphenyl)benzotriazole, 2-(3'-tertbutyl-2'-hydroxy-5-methylphenyl)-5-chlorobenzotriazole, 2-(3',5'-di-tertbutyl-2'-hydroxyphenyl)-5-chlorobenzotriazole, 2-hydroxy-4-n-octyloxybenzophenone, bis[O-ethyl (3,5-di-tertbutyl-4-hydroxybenzyl)]phosphonate, etc., and PA2 (4) about 0-5% and preferably about 0.5-3% by weight of a colorant dispersible in polyolefins such as a high density polyethylene with a melt index in the range of about 0.2-30 g/10 min. and/or polypropylene with a melt flow rate in the range of about 20-50 g/10 min. PA2 (1) about 0-10% and preferably about 0.5-5% by weight of an opacifier such as TiO.sub.2 having a particle size able to pass through a 200 mesh screen and preferably through a 325 mesh screen, PA2 (2) about 0-20% and preferably about 0.5-15% by weight of a fire retardant composition comprising one or more polyhalogenated organic compounds and antimony trioxide, PA2 (3) about 0-3% and preferably about 0.5-2% by weight of an ultraviolet light stabilizer such as nickel bis[O-ethyl (3,5 di-tertbutyl-4-hydroxybenzyl]phosphonate, 2-(2-hydroxy-5-t-octylphenyl)benzotriazole, 2-(3'-tertbutyl-2'-hydroxy-5-methylphenyl)-5-chlorobenzotriazole, 2-(3',5'-di-tert-butyl-2'-hydroxyphenyl)-5-chlorbenzotriazole, 2-hydroxy-4-n-octyloxybenzophenone, etc., and PA2 (4) about 0-5% and preferably about 0.5-3% by weight of a colorant dispersible in polyolefins, such as high density polyethylene having a melt index in the range of about 0.20 to 30 g/10 min. and/or polypropylene with a melt flow rate in the range of 20 to 50 g/10 min. PA2 (1) about 0-10% and preferably about 0.5-5% by weight of an opacifier such as TiO.sub.2 able to pass through a 200 mesh screen, and preferably through a 325 mesh screen, PA2 (2) about 0-20% and preferably about 0.5-15% by weight of a fire retardant composition comprising one or more polyhalogenated organic compounds and antimony trioxide, PA2 (3) about 0-3% and preferably about 0.5-2% by weight of an ultraviolet light stabilizer for polyolefins such as nickel dibutyl dithiocarbamate, 2-(2-hydroxy-5-t-octylphenyl)benzo-triazole, 2-(3'-tertbutyl-2'-hydroxy-5-methylphenyl)-5-chlorobenzotriazole, 2-(3',5'-di-tertbutyl-2'-hydroxyphenyl)-5-chlorobenzotriazole, 2-hydroxy-4-n-octyloxy-benzophenone, nickel bis(O-ethyl(3,5-di-tertbutyl-4-hydroxybenzyl))phosphonate, etc., and PA2 (4) about 0-5% and preferably about 0.5-3% by weight of a colorant dispersible in polyolefins such as high density polyethylene having a melt index in the range of about 0.20 to 30 g/10 min. and/or polypropylene having a melt flow rate in the range of about 20 to 50 g/10 min.
McConnell et al. (`759) does not disclose the use of similar coating compositions for an extrusion coating process nor the use of polyolefins and particularly polypropylene as coatable substrates. In the relevant art, curtain coating is a different and distinct coating process from that of an extrusion coating process. Each requires coating compositions having very different rheological properties. A principal limitation of curtain coating is that useful coating compositions must be sufficiently fluid to fall freely and sufficiently cohesive to present a continuous film to the substrate.